1. Field of the Invention
This invention relates to a process and apparatus for combustion of carbon black and natural gas in a combustion chamber to produce a luminous flame and maintain low-pollutant emissions. In particular, this invention relates to a process and apparatus for combustion of a carbon black enriched gaseous hydrocarbon fuel.
2. Description of the Prior Art
In many high temperature industrial applications, such as glass melting furnaces, it is desired to provide a highly luminous flame to improve radiant heat transfer rate to the furnace load resulting in increased furnace production rate and increased furnace thermal efficiency. When generating such highly luminous flames, environmental considerations require that pollutant emissions, including nitrogen oxide emissions, be maintained at a low level. Highly luminous flames are typically generated in the combustion of both coal and fuel oils. However, combustion of solid and liquid fuels is difficult to control and typically results in high pollutant emission rates requiring treatment of the flue gases to reduce pollutant emissions to an acceptable level. The combustion of gaseous hydrocarbon fuels, such as natural gas, produces flames having lower luminosity than flames produced by solid or liquid fuel combustion. However, combustion of gaseous hydrocarbon fuels generally produces substantially lower pollutant emissions than the combustion of solid or liquid fuels, and thus, gaseous hydrocarbon fuels, such as natural gas, are preferred for many industrial applications.
Methods for producing highly luminous flames in the combustion of gaseous hydrocarbon fuels are known in the prior art. One such method is simply to combust the gaseous hydrocarbon fuel under fuel rich conditions, thereby generating large amounts of carbon monoxide and some soot, both of which have high emissivities. However, this technique also produces flue gases containing high levels of pollutant emissions which must be removed, or otherwise eliminated, before being exhausted into the atmosphere.
U.S. Pat. No. 4,761,132 teaches a two-stage process and apparatus for producing a highly luminous flame in which a portion of the total fuel to be combusted is cracked in a cracking chamber under fuel rich conditions with oxygen rich gas and the cracked products including uncracked fuel, carbon monoxide, hydrogen, carbon dioxide, water, soot, some inerts, and a second portion of fuel are combusted in a combustion chamber.
U.S. Pat. No. 3,656,878 teaches a high luminosity burner in which products of combustion, which include soot particles, are burned with a second fuel such as natural gas. Incomplete combustion of a first fuel in a diffusion flame is used to produce a controlled quantity of solid soot particles which, along with other products of the diffusion flame combustion, move downstream where they are again combusted with a gaseous fuel in the presence of excess air to produce a secondary flame which has luminosity greater than the luminosity normally associated with the combustion of gaseous fuels.
U.S. Pat. No. 3,827,851 and related U.S. Pat. No. 3,859,935 relate to a combination oil, gas and/or solids burner. The '851 patent teaches operation of the burner apparatus with oil, gas and/or particulate solid material in which the particulate solid fuel is preferably wood, plastic, coal or other suitable substitutes which can be formed into relatively small particle sizes so that the fuel burns in suspension. The particulate solid fuel is introduced into the combustion chamber by either blowers, screw augers, conveyer belts or the like. The '935 patent teaches a process for using the apparatus taught by the '851 patent in which a combination burner structure is provided with an inner burner for oil and/or gaseous fuels, mounted with a refractory primary combustion chamber and a wood air mixture passageway surrounding the oil and/or gas burner. During the process, particulate combustible material is introduced into the combustion chamber after having been dried.
U.S. Pat. No. 4,015,951 discloses fuel pellets for burning in industrial applications and a method for making such fuel pellets from organic fibrous materials. U.S. Pat. No. 4,249,471 teaches a method and apparatus for producing a combustible mixture of a solid fuel pellet made from organic fibrous material, as disclosed in the '951 patent, and a flammable gas or liquid fuel in which a blower forces the pulverized sold fuel into a conduit, the stream of pulverized fuel being tangentially added to the gaseous fuel entering a center conduit of the apparatus.
U.S. Pat. No. 4,780,136 teaches a method of injecting combustion resistant fuel into a blast furnace in which a measured portion of combustion resistant fuel is injected into a stream of hot blast air and a gaseous fuel is injected into the hot blast air independent of the pulverized fuel, the gaseous fuel being supplied to an outer peripheral area of the pulverized fuel.